Atomic Absorption Spectroscopy

Atomic absorption spectroscopy is based on the same principle as the flame test used in qualitative analysis.

 The high temperature of the flame excites a valence electron to a higher-energy orbital.  The atom then emits energy in the form of light as the electron falls back into the lower energy orbital (ground state). The intensity of the absorbed light is proportional to the concentration of the element in the flame.

quantitative analysis Atomic Spectra

 Each element has a characteristic spectrum. Example: Na gives a characteristic line at 589 nm.  Atomic spectra feature sharp bands. There is little overlap between the spectral lines of different elements.

Atomic absorption spectroscopy and atomic emission spectroscopy are used to determine the concentration of an element in solution.

Applying Lambert-Beer’s law in atomic absorption spectroscopy is difficult due to  variations in the atomization from the sample matrix  non-uniformity of concentration and path length of analyte atoms. Concentration measurements are usually determined from a calibration curve generated with standards of known concentration. Concentration measurements are usually determined from a calibration curve generated with standards of known concentration.

Schematic diagram of an atomic absorption spectrometer

Light Source Hollow-cathode lamp: The cathode contains the element that is analysed. Atomization Desolvation and vaporization of ions or atoms in a sample: high-temperature source such as a flame or graphite furnace  Flame atomic absorption spectroscopy  Graphite furnace atomic absorption spectroscopy

1- Flame atomic absorption spectroscopy: Sample introduction:

Process in a Flame AA M* M + + e _ M o M * MA M o + A o Solid Solution Ionization Excitation Atomization Vaporization

Graphite furnace atomic absorption spectroscopy Sample holder: graphite tube  Samples are placed directly in the graphite furnace which is then electrically heated.  Beam of light passes through the tube.

Basic Graphite Furnace Program THGA Three stages: 1. drying of sample 2. ashing of organic matter 3. vaporization of analyte atoms to burn off organic species that would interfere with the elemental analysis. transversely heated graphite atomizer

Basic Graphite Furnace Program THGA Temp Time Dry 1 Pyrolysis Atomization Clean Dry 2

The autosampler capillary tip

GraphiteFlame Advantages Solutions, slurries and solid samples can be analyzed. Much more efficient atomization greater sensitivity Smaller quantities of sample (typically 5 – 50 µL) Provides a reducing environment for easily oxidized elements Inexpensive (equipment, day-to-day running) High sample throughput Easy to use High precision Disadvanta- ges Expensive Low precision Low sample throughput Requires high level of operator skill Only solutions can be analyzed Relatively large sample quantities required (1 – 2 mL) Less sensitivity (compared to graphite furnace)

Applications of Atomic Absorption Spectroscopy  water analysis (e.g.Ca, Mg, Fe, Si, Al, Ba content)  food analysis; analysis of animal feedstuffs ( e.g. Mn, Fe, Cu, Cr, Se, Zn)  analysis of additives in lubricating oils and greases (Ba,Ca, Na, Li, Zn, Mg)  analysis of soils  clinical analysis (blood samples: whole blood, plasma, serum; Ca, Mg, Li, Na, K, Fe)

Detection Limits

Atomic Absorption Overview